7.11B Explain how thermoregulation takes place, with reference to the…

The idea

Thermoregulation is coordinated negative feedback. The hypothalamus detects blood temperature and triggers responses. In the dermis, sweat glands release sweat that evaporates and cools the skin; arterioles supplying skin capillaries vasodilate (more blood near the surface, more heat lost) when hot, and vasoconstrict (less blood near the surface, heat conserved) when cold; hair erector muscles raise hairs to trap an insulating air layer when cold and lower them when hot. The epidermis forms the outer barrier and contains keratin, reducing water loss and protecting underlying tissue; it also holds the sweat duct openings. Match each structure to its response and the direction of heat transfer.

What earns the marks

• The hypothalamus detects changes in blood temperature and coordinates the body's responses as a control centre.
• In the dermis, sweat glands produce sweat; evaporation of sweat from the skin surface removes heat and cools the body.
• Dermal arterioles vasodilate when hot, sending more blood to surface capillaries so more heat is lost by radiation; they vasoconstrict when cold to reduce heat loss.
• Hair erector muscles in the dermis contract when cold to raise hairs and trap an insulating layer of air; they relax when hot.
• The epidermis is the outer protective layer containing keratin, reducing water loss and protecting underlying tissues, and sweat ducts pass through it to the surface.
• Responses are coordinated by negative feedback so body temperature returns towards the optimum.

Common mistakes and how to put them right

• Saying sweat 'contains heat' that is removed.

  Put it right: It is the evaporation of sweat that transfers heat energy away from the skin.

• Confusing vasodilation and vasoconstriction.

  Put it right: Vasodilation widens arterioles (more heat lost when hot); vasoconstriction narrows them (heat conserved when cold).

• Naming the skin as the control centre.

  Put it right: The hypothalamus detects and coordinates; the skin carries out the responses.

• Saying hairs themselves generate heat.

  Put it right: Raised hairs trap air, which insulates and reduces heat loss.

Exam tips

• Always link a structure to its response and then to the effect on heat loss or gain.
• Use the correct terms vasodilation and vasoconstriction and say which happens when hot or cold.
• State that the hypothalamus detects blood temperature and coordinates responses, not the skin.